Han Bingjun, Wang Xiaomao, Zheng Jianzhong, Liang Shuai, Xiao Kang, Yu Jinlan, Qian Zhi, Huang Xia
College of Resources and Environment , University of Chinese Academy of Sciences , Beijing 100049 , Beijing , China.
College of Environmental Science and Engineering , Beijing Forestry University , Beijing 100083 , Beijing , China.
Langmuir. 2019 Nov 26;35(47):15009-15016. doi: 10.1021/acs.langmuir.9b02508. Epub 2019 Nov 13.
While the contact angle is a well-applied indicator of membrane hydrophobicity and surface energy, the interference of surface roughness and porosity in contact angle measurement and surface energy calculation has been long neglected in the field of porous membrane study. We propose an improved method to straightforwardly derive the surface energy of the porous membrane from contact angles with the interference effect corrected. A linearized model was established combining the Young-Dupré and Cassie-Baxter equations, from which the surface energy (Lifshitz-van der Waals and Lewis acid/base components) and roughness index (surface area difference) can be solved simultaneously at a given porosity using contact angles measured with a set of standard polar/nonpolar test liquids. The model solution was examined using hydrophilic microfiltration membranes with different pore morphologies (including perforated plate-like PCTE, irregular particulate bed-like PVDF, and fibrous mesh-like PTFE membranes), with the robustness of the results evaluated via Monte Carlo simulation. In comparison with the verified results of the model solution, it was found that the Lifshitz-van der Waals Lewis acid/base energy values for the tested membranes would deviate by 50-87, 30-160, and 52-97%, respectively, if surface roughness and porosity were neglected in the calculation. The profound effect of roughness and porosity on surface energy determination was further confirmed via theoretical analysis of the Young-Dupré and Cassie-Baxter relationships. This improved approach may apply to the surface energy characterization of hydrophilic rough porous membranes (e.g., hydrophilic microfiltration membranes).
虽然接触角是膜疏水性和表面能的一个广泛应用的指标，但在多孔膜研究领域，表面粗糙度和孔隙率对接触角测量和表面能计算的干扰长期以来一直被忽视。我们提出了一种改进方法，可在校正干扰效应的情况下，直接从接触角推导出多孔膜的表面能。结合杨氏-杜普雷方程和卡西-巴克斯特方程建立了一个线性化模型，利用一组标准极性/非极性测试液体测量的接触角，在给定孔隙率下可同时求解表面能（里夫希茨-范德瓦尔斯分量和路易斯酸碱分量）和粗糙度指数（表面积差）。使用具有不同孔形态的亲水性微滤膜（包括穿孔板状聚三氟氯乙烯、不规则颗粒床状聚偏氟乙烯和纤维网状聚四氟乙烯膜）对模型解进行了检验，并通过蒙特卡罗模拟评估了结果的稳健性。与模型解的验证结果相比，发现如果在计算中忽略表面粗糙度和孔隙率，测试膜的里夫希茨-范德瓦尔斯路易斯酸碱能值将分别偏差50-87%、30-160%和52-97%。通过对杨氏-杜普雷关系和卡西-巴克斯特关系的理论分析，进一步证实了粗糙度和孔隙率对表面能测定的深远影响。这种改进方法可能适用于亲水性粗糙多孔膜（如亲水性微滤膜）的表面能表征。
